Steve Hitchcock, Tim Brody, Jessie M.N. Hey , and Leslie Carr
Digital preservation can encompass a range of activities, from simple replication and storage to more complex transformation, depending on the assessed value and risk to the target content. These activities require planning and, in most cases, begin with a need to know the technical format of the target content. In this case, the target is the content deposited in institutional repositories (IRs). The Preserv project  set out to investigate the use of The National Archives' (TNA) PRONOM-DROID service (PRONOM is the online registry of technical information; DROID is the downloadable file format identification tool) for file format identification on two pilot IRs using EPrints software, and instead produced format profiles (Preserv profiles) of over 200 repositories presented via the Registry of Open Access Repositories (ROAR). Thus a primary element of preservation planning has been shown to be possible based on a standard Web interface (OAI) and no formal arrangement between repository and provider. The implications of this go beyond the numbers towards a reconceptualisation of repository preservation service provider models. Repositories and providers can shape preservation services at different cost levels that could range from comprehensive 'black-box' preservation to pick-and-mix lightweight Web-based services that build on the common starting point, format identification. This article describes the evolution of a series of models that have informed progress towards this conception of flexible and distributed preservation services for IRs.
How are institutional repositories (IRs) to preserve the digital content for which they accept responsibility? Until now, much emphasis has been placed on the role of repository software. Two of these software applications, notably DSpace  and Fedora , have promoted support for preservation as a key feature. In contrast, the first software designed for IRs, EPrints , has until now offered less explicit support for preservation. In truth, reliance on repository software alone will not be sufficient: "it seems obvious that no existing software application could serve on its own as a trustworthy preservation system. Preservation is the act of physically and intellectually protecting and technically stabilizing the transmission of the content and context of electronic records across space and time, in order to produce copies of those records that people can reasonably judge to be authentic. To accomplish this, the preservation system requires natural and juridical people, institutions, applications, infrastructure, and procedures." (Wilczek and Glick 2006)
Repository support teams need to engage in preservation management, planning and policy. Even then, more specialised technical preservation tasks might best be outsourced. The JISC-funded  Preserv project has been investigating with possible preservation service providers just what services might serve IRs and how they might be delivered. This article illustrates the models that have been developed to inform the investigations, and shows how the general preservation service provider model has evolved, based on the project's experiences, away from the idea of a monolithic service provider towards more discrete, flexible and distributed Web-based preservation services.
First we need to explain what is meant by the term 'preservation' as it applies to the digital objects and environments with which Preserv is concerned.
What is 'preservation'?
Most collectors know that organising and storing physical collectibles is likely to provide more assurance of retrieval than simply throwing items on a coffee table. This is the equivalent of depositing an electronic paper in an IR rather than simply uploading it to a personal server and Web page. The organisation of the IR together with the commitment of the sponsoring institution will provide greater assurance than a server with unknown support looking forward. Simple storage is hardly a complete solution, however. In the long term, even physical materials suffer some degradation. The equivalent process of degradation for digital materials is typically caused by format obsolescence due to changes in software applications technology, often regarded as a rapid process in comparison with degradation of physical materials and can be ameliorated by specialised technical processes such as format migration. In both cases, the extended risks to physical and digital materials might be most cost-effectively tackled by specialist preservation services. For information materials like books and journals, these services have traditionally been offered by libraries and archives, and such organisations might be well positioned to serve digital sources too.
Digital preservation thus covers a wide range of activities, from storage to transformation, depending on the nature of the resources and the source, and the range of preservation services could be equally wide. Since such services are not yet widely practised or available, a useful starting point is to consider what is known about the target content in IRs.
Evolution of institutional repositories
It is helpful to consider what IRs are, what they do and where the idea comes from, because this is a relatively recent development.
An IR provides access to the content and materials produced by members of that institution, typically a university or other educational establishment. The impetus for IRs was boosted by the Open Archives Initiative (OAI) in 1999, not to be confused in preservation terms with the Open Archival Information System (OAIS 2002, Hirtle 2001). Institutionally based, or more typically departmental, 'archives' were known before this, especially in areas such as computer science and economics that were served by the Networked Computer Science Technical Reference Library  and Research Papers in Economics , respectively. OAI introduced the Protocol for Metadata Harvesting (OAI-PMH) to provide common services that could operate over more general, independent sites (Lynch 2001). Search is the most obvious example of such a service. OAI-PMH enables compliant sites to be interoperable, thus making institutional, rather than only disciplinary, repositories visible and viable. For the first time institutions such as universities have the ability to capture, store and disseminate copies of the published work of their own researchers. The significance of this cannot be underestimated.
OAI was aimed initially at eprint archives (Van de Sompel and Lagoze 2000), and although the protocol was soon applied to other digital library content, the first software to support it was EPrints, developed at Southampton University and on which we base our work. EPrints is software for building IRs that capture and provide open access to an institution's research outputs and publications, which are deposited directly by authors in principle using the version they created, a process known as 'self-archiving'. One of the consequences of this approach is that IRs incur low cost per item deposited, in turn creating the conditions for open access: immediate and permanently free access to published research papers. As such, where digital preservation might generally be concerned with preserving access, for IRs it is concerned with preserving open access, which has cost implications.
EPrints software first appeared in 2000, and an OAI-PMH 1.0-compliant version was announced on the same day this breakthrough version of the protocol was unveiled in January 2001 (Harnad 2001, OAI 2001). This application to IRs was reinforced with the emergence of DSpace software the following year, and other IR software applications have followed since.
Growth in the number of IRs has accelerated since 2002 and, despite some lag in time, there has been corresponding growth in the volume of content in IRs (Figure 1), as revealed by the Registry of Open Access Repositories (ROAR ). According to data recorded by a wider registry of OAI-compliant repositories, OAIster, there was a 25% growth in the number of such repositories (up to 726), and a 59% increase in the number of records in those repositories (up to 9,931,910) between December 31, 2005 and the same date in 2006 (Suber 2007).
The fundamental requirements of repositories were characterised by Heery and Anderson (2005):
IRs are additionally characterised by the institution, and the type of content it requires and permits to be deposited, and for what purpose, most commonly research outputs for open access.
This description of what IRs are and what they represent is not to say that the role and target content of IRs won't evolve legitimately and in an informed way to serve institutional needs and research purposes, as suggested by Dempsey (2006). Other types of content, such as research data sets (Lyon et al. 2004), theses, reports and multimedia can be deposited and managed within EPrints-based IRs.
Suber (2006) predicted "a continuing tension between the narrow conception of institutional repositories (to provide open access for eprints) and the broad conception of IRs (to provide open access for all kinds of digital content, from eprints to courseware, conference webcasts, student work, digitized library collections, administrative records, and so on, with at least as much attention on preservation as access). But I have to predict that the broad conception will prevail. Universities that launch general-purpose archiving software will have active constituents urging them to take full advantage of it."
Taking the age profile of most repositories into account, the need for preservation is perhaps less critical than for older digital content sources, but other factors such as growth and diversity point towards a more urgent need to plan for preservation by the more content-rich repositories.
Three OAIS preservation models for IRs
Having defined the target content for preservation services in terms of IRs, we can consider the types of services that can be offered. The OAIS reference model (Figure 2a) provides a framework in which we can construct these services (OAIS 2002). At a very general level it can be seen that IRs provide a similar range of functionality as found in OAIS input and output, data management and storage. OAIS imposes more formality and discipline on these processes for the purpose of long-term preservation. Thus deposit becomes ingest, and we are concerned with archival storage, all enveloped by preservation planning, administrative and management roles. To understand these distinctions and these support processes, see the excellent Cornell tutorial (2003). Information in this system is managed in packages: submission information packages (SIPs) at point of ingest, archival information packages (AIPs) in the preservation store, and dissemination information packages (DIPs) for access by users or other services.
Within the types of services we could construct, we wish to support a range of business models to allow IRs some flexibility in managing the preservation risk in terms of their real resources, leading to the following proposed models:
The basis of the three service models in the formal OAIS model are apparent in Figure 2. Representations of the OAIS reference model are ubiquitous in the digital preservation literature and may differ in presentation if rarely in detail; for reference, this version (Figure 2a) was taken from a presentation by Day (2003). The changes in the service models are shown in red and are all focussed on the ingest/data management/archival storage roles and the relations between these as shown by the connecting arrows. Since access is a primary feature of IRs, it has been assumed that support services would not need to replicate this function. In the service provider model, a case could be made to re-introduce the arrow connecting the service provider and the access point (e.g., EVIE 2006), depending on the agreement between the IR and service provider partners, and the form of the preservation service.
The three models illustrated have no specific costs attached, but represent a hierarchy in terms of level of cost (from Figure 2b highest down to 2d) that might be incurred to support preservation, based on Chapman's (2003) observation: "though quantity, quality and size of the digital materials ingested has an impact on scale, the cost of long-term digital sustainability correlates more to the range of digital services offered." The range of services offered by the service provider (Figure 2b) is clearly potentially greater and more flexible than the latter two, with the software model providing a baseline requirement.
Other models might include federated and network models. These models are beyond the immediate scope of this article, but it is worth highlighting some examples. A prominent federated example is LOCKSS (Rosenthal et al. 2005), which focusses on journal applications rather than more heterogeneous collections such as in IRs, and is predicated on the idea that the risk of data loss can be reduced simply by copying and transferring content between trusted partners. The MetaArchive project  has extended the LOCKSS approach to at-risk digital content from various digital repositories focussing on the culture and history of the American South.
Integration of Storage Resource Broker (SRB) with DSpace (Declerck and Frymann 2004) illustrates a network preservation approach. "SRB is a very robust, sophisticated storage manager which offers essentially unlimited storage and straightforward means to replicate (in simple terms, backup) the content on other local or remote storage resources." (Tansley et al. 2005). Similarly the Shared Infrastructure Preservation Models project investigated how dissemination of repository content can be 'piggybacked' on top of existing network services such as email and Usenet traffic: "Long-term persistence of the replicated repository may be achieved thanks to current policies and procedures that ensure that email messages and news posts are retrievable for evidentiary and other legal purposes for many years after the creation date. While the preservation issues of migration and emulation are not addressed with this approach, it does provide a simple method of refreshing content with various partners for smaller digital repositories that do not have the administrative resources for more sophisticated solutions." (Smith et al. 2006)
Preservation service provider model
The preservation service provider model was broadly outlined in terms of shared, or third-party, preservation services by Beagrie (2002), while RLG-OCLC (2002) reported the need for third-party preservation services to fulfill the role of trusted digital repositories. James, et al. (2003) proposed this model for IRs. Referring to this as a disaggregated OAIS-compliant model, Knight (2005) extended the idea to a model-based, rather than evidence- or experience-based, analysis. Knight presented a detailed breakdown of the model and workflow from the service provider's perspective. In this case, the service provider is represented by the Sherpa-DP project. Experience is likely to bring both more complexity and more clarity.
One particular type of content already subject to emerging preservation services is that of electronic theses and dissertations (ETDs). While theses have long been collected by national libraries, work at the German National Library is advancing towards providing a preservation framework for ETDs (Wollschlaeger 2006). The Repository Bridge project demonstrated how ETDs could be harvested using OAI and METS from Welsh IRs to a Fedora-based repository at the National Library of Wales (Lewis and Bell 2006), while Santhanagopalan et al. (2006) harvested OAI content to a LOCKSS network involving six Networked Digital Library of Theses and Dissertations (NDLTD) repositories.
Can this approach be extended to all types of content in IRs, not just ETDs? The National Library of the Netherlands (Koninklijke Bibliotheek, KB) announced  that it will preserve the open access repositories in the country's DAREnet network. No technical details are available yet, although the KB has for some time been archiving e-journals (Steenbakkers 2004), and it might be expected there will be similarities in its approach for IRs.
In the first instance, these initiatives, as with the federated and network examples, principally tested mechanisms to transfer content between originating repositories and preservation services or preservation networks. Moving the focus away from ETDs as the source content, the Archive Ingest and Handling Test (AIHT) similarly investigated the effects of content transfer. The AIHT practical preservation strategy will require "mechanisms for continuous transfer of content from the wider world into the hands of preserving institutions. The AIHT is designed to test the feasibility of transferring digital archives in toto from one institution to another" (Shirky 2005). This approach involving more than one agency in content management parallels our service provider model outlined below. AIHT reveals important practical experience, although there are some differences with anticipated preservation service models for IRs. For example, in AIHT:
Of the AIHT exemplars, that described by DiLauro et al. (2005) is instructive for IR applications, being concerned with ingest into, and transfer between, Fedora and DSpace-based archival stores.
While replication and storage can provide some support for preservation, it is not a complete solution in the longer term because the effects of format obsolescence require more expert support. Given the low age of most IRs, this has not yet become a major issue, and there are few examples currently of preservation services that go beyond simple storage. Cornell's File Format and Media Migration Pilot Service is an interesting exception, since it attempted to retrieve older legacy materials and was concerned not just with format obsolescence but also media obsolescence, for example, the problem of old disc and tape technologies (Entlich and Buckley 2006). Perhaps the most revealing point is left to the penultimate paragraph, however: "We believe a superior alternative is to establish institutional repositories in which faculty are encouraged to deposit their work."
The service provider model to be adopted in the Preserv project was developed in stages, as described by Hitchcock (2005). This model is formalised in Figure 3. A notable feature of the illustrated model is the integration of an automated file format identification tool, PRONOM-DROID, developed by The National Archives (TNA) in the UK (Brown 2005). The service provider model again fits well with an OAI application, which as we have seen is core to IR software, because OAI is predicated on the data provider-service provider relationship (Lynch 2001). The archival storage, or service provider, element in principle covers the full range of preservation services, from bit-level storage to migration and emulation. At this stage, this can be viewed as a 'black box' approach from the IR perspective, because the preservation activities are assumed to be performed entirely by the service provider based on an agreed plan. We will soon begin to see this aspect of the model change, however, towards a more interactive relationship between preservation service and IR.
As in Knight (2005), the Preserv model, as presented, easily lends itself to analogy with the ubiquitous OAIS representation. In terms of the main OAIS functionality ingest, data management, storage, dissemination, etc. these models highlight how responsibilities might be shared between partners. For example, in the service provider model the IR could be OAIS-compliant, but it need not necessarily be if the service provider delivers that compliance. At the other extreme, in the software model where there is no other partner, the IR clearly has to be OAIS-aware to provide a minimal level of compliance. There are essentially three variations:
In IR terms, the formalisation of the deposit interface to embrace the requirements of OAIS ingest has particular significance: "until it becomes common practice to integrate digital stewardship and preservation concerns into the entire digital content lifecycle especially front-end content creation most digital preservation workflows intended to be inclusive will be reactive instead of prescriptive." (Anderson et al. 2005). IRs are some way from being able to impose on authors content creation rules to support preservation.
In Preserv one service provider partner is the British Library (BL), which of course will offer an OAIS service. Thus the second of the three variations is most likely to be the case. Figure 4 shows two simplified, co-joined OAIS models representing the IR and the service provider. The OAIS administrative functions are shown as shared between the two partners pending further investigation into this model to determine practical allocations.
Figure 4 also explodes the service provider into a range of optional services, which were informed by the BL. While the first two byte storage and transformation focus on data ingest, the latter two services rendering and emulation are concerned with dissemination and presentation. These services further differentiate the cost options. What is striking is that each of these services is different to the extent it changes the relationship between the service provider and the repository. Preservation need no longer be a monolithic service in this model. By choosing services based on a developed institutional profile this potentially changes the relation from a simple 'you give us the data and we store it' to a more tailored and interactive partnership. In the next section we see how this more flexible model can be developed further.
Distributed preservation services: The impact of PRONOM-ROAR
There are sometimes moments in a project's development when hypothetical models are overturned by practical experience. The trick is to spot this tipping point and to adapt the model against the prevailing wisdom of the project. Preserv encountered such a moment and was transformed.
We had begun to implement the model of Figure 3, starting with the use of PRONOM-DROID to profile the formats contained in two partner repositories at Oxford and Southampton universities. This proceeded pretty much to plan. Although not all formats were successfully recognised initially, we were able to work locally with the repository managers, and feedback to TNA led to refinements to the PRONOM-DROID format database and ID tool. The problem was largely resolved. The issue we now faced was where to place format ID in the schematic: within the author deposit interface to the IR, a notoriously sensitive area for IRs, or as a service to the repository manager.
A secondary issue was scalability to many more repositories. As we have seen, ROAR provides important quantitative data on the growth of repositories. Data to ROAR is provided by an OAI harvesting service called Celestial. Both are developed at Southampton University independently of Preserv by Tim Brody, a member of the project team. Brody moved the format ID process from the repository to the OAI service provider, running DROID against the content harvested by Celestial, and presenting a rudimentary interface to the results, shown as links to Preserv profiles, through ROAR. By combining PRONOM-DROID and ROAR through Web services, the number of repositories with format profiles leapt from two to over 200. The features of PRONOM-ROAR are explained in an illustrated guide .
Now the thinking about preservation services changes. First the relation is no longer between PRONOM-DROID and a repository, but with an intermediate service. Second, accurate format ID may be a prerequisite for preservation planning, but alone it is not a solution, so the question is what to do with this information; how to layer on additional, value-added preservation services. If format ID can be provided as a discrete service, presumably it is possible to provide other services as discrete components via Web services, perhaps from multiple service providers.
We already have some clues as to the type of discrete preservation services that might be provided (Figure 4). In addition, a structure that might lend itself to preservation Web services was emerging from TNA's Seamless Flow programme . TNA initiated this programme in an effort to reengineer workflow in the creation, management and preservation of electronic records demanded by the impact of increasing volume and the need to widen access (in this case, not in response to open access but to meet freedom-of-information requirements). One application of this approach was illustrated by Brown (2005). Applying this approach to Preserv led to the following structured process for active preservation aimed at repository content that enables the contributing service components to be identified:
If we have repositories, growing content, services to access that content and prospective preservation service providers, the one missing component is a preservation services testbed, a scalable, realistic and effective environment to test tools and services. This might be provided by the PLANETS project , an EU-wide project in which both TNA and BL are partners.
Others have described service-oriented preservation architectures. PANIC (Preservation webservices Architecture for Newmedia and Interactive Collections) proposed a way of describing and discovering preservation Web services using the Semantic Web (Hunter and Choudhury 2005). This anticipates multiple services from multiple providers without specifying what or who, and doesn't take account of possible market mechanisms, which may become a key factor if services are to be sustainable. Ferreira et al. (2006) describe a preservation service architecture that could in principle use a combination of service providers and Web service agents, although providing little in the way of evaluation to show how effective this approach might be.
Based on experience with PRONOM-ROAR, and adopting ideas leading towards distributed Web preservation services from Seamless Flow and other projects, we have updated the service provider schematic from Figure 3 to show repository services and selectable preservation services (Figure 5).
Compared with Figure 3, the updated version displays the classified preservation services identified above, with an additional bitstream, or storage-based, preservation package. For simplicity, these services are shown with two-way interaction with, in principle, any number of preservation service providers. The generic machine interface to the IR is replaced with an OAI harvester linked to a service with a human-readable interface. This necessitates that the bi-directional connecting arrow between the service provider and repository via the machine interface reverts to an arrow in a single direction from repository to harvester. Completion of the feedback loop for the return of metadata and transformed content to the repository from the services is represented by a direct connecting arrow between the two. Critically, PRONOM-DROID has moved from the repository user/author interface to somewhere between harvester and interface repository services, as in the case of PRONOM-ROAR.
How will this schematic stand up to practical examination? There is at least one example of a service in action, if still experimental. Curtis (2006) describes the Automated Obsolescence Notification System (AONS), a system to analyse digital repositories and determine whether any digital objects contained within them may be in danger of becoming obsolescent. This is another application that uses preservation information about file formats taken from PRONOM. The approach is designed to work primarily with DSpace repositories, although in general terms the work is examining the interface between repository software and registries such as PRONOM. In terms of the services outlined in Figure 5, this comes closest to technology watch, part of preservation planning.
Distributed preservation services require further investigation and raise further questions about the interaction of service providers and client repositories:
While there may be some emerging consensus on the range of services that may be needed, the primary requirement is for market testing conditions. The market for repository services is not well formed or structured. The number of repositories is growing internationally but these are at different stages of development in terms of content, institutional backing and funding and, therefore, in policy. The market for preservation services among IRs will be determined by repository policy. A survey of repositories with a Preserv profile discovered that none had a formal preservation policy (Hitchcock et al. 2007). Preservation policy should emerge naturally from general institutional and repository policy. Repository directory OpenDOAR discovered that only one-third of repositories have any kind of policy (Millington 2006). This suggests that repositories may be waiting for clear guidance on preservation from trusted service providers, and this allows scope for the services proposed in this article. It should not be assumed, however, that service providers have an entirely blank canvas to work with. The Preserv survey also revealed that, even without a policy, repositories are making decisions with preservation consequences, for example, restrictions on file formats that could be deposited. Service providers will need to be aware of the practicalities facing repositories, including prior decisions, in scoping services.
The Preserv project has reached the end of its initial period of funding, and will continue this work in a second phase (Preserv 2) starting soon, again supported by JISC. The signs are that preservation service providers will emerge to take advantage of Web infrastructure to deliver tailored and cost-effective services driven by institutional repositories' increasing awareness and need for preservation support.
Notes and Links
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Copyright © 2007 Steve Hitchcock, Tim Brody, Jessie M.N. Hey and Leslie Carr